We present the results of the atmospheric optical turbulence ( OT ) measurements performed atop Mt .
Shatdzhatmaz at the installation site of new 2.5-m telescope of Sternberg Astronomical Institute .
Nearly 300 000 vertical OT profiles from the ground up to an altitude of 23 km were obtained in the period November 2007–June 2013 with the combined multi-aperture scintillation sensor ( MASS ) and differential image motion monitor ( DIMM ) instrument .

The medians of the main OT characteristics computed over the whole dataset are as follows : the integral seeing \beta _ { 0 } = 0.96 arcsec , the free-atmosphere seeing \beta _ { free } = 0.43 arcsec , and the isoplanatic angle \theta _ { 0 } = 2.07 arcsec .
The median atmospheric time constant is \tau _ { 0 } = 6.57 \mbox { ms } .
The revealed long-term variability of these parameters on scales of months and years implies the need to take it into account in astroclimatic campaign planning .
For example , the annual variation in the monthly \theta _ { 0 } estimate amounts up to 30 % while the time constant \tau _ { 0 } changes by a factor of 2.5 .

Evaluation of the potential of Mt .
Shatdzhatmaz in terms of high angular resolution observations indicates that in October–November , this site is as good as the best of studied summits in the world .